> > I just thought of something: If you put a container of water in a freezer, it will crystallize from the outside and inwards, causing the core to freeze last. But since water expands when it freezes, this must seriously mess up the crystalline structure, since the expanding liquid core will be "shut in" by the surrounding ice. [...]
> >
> > Trav"inquisitive mind"holt.

Ice, when frozen under the conditions described, crystallizes in a clear and transparent zone along the outer edges of the container, and with a white mass of bubbles in the central portion. This white mass is dissolved oxygen being forced out of the water as it freezes. The outer zone is clear because when it first starts freezing along the walls, the water molecules have sufficient space to H-bond themselves into a neat, regular lattice structure. I would call this region the "columnar zone" because the crystals are more organized at this point, and growing directionally inwards.

The expanding liquid core does have a disturbed structure relative to the outer crystals. Core crystals freeze in an equiaxed type of structure (meaning they are non-directional, having the same direction in all directions). As the core expands as it freezes, it forces the central part of the liquid upwards in the kind of 'bump' you'd see in a bottle of frozen homemade soup broth.


> > How would it look if you were able to freeze it from the center and outwards? Would it be much different?
> >

The central portion would be clear (or at least, the white oxygen mass wouldn't be concentrated there). Opaque bubbles would be dispersed along the sides of the container. At the top of the container, the surface of the ice mass would be raised in a concave "bowl shape" since the expanding edges freeze last.

Incidentally, ice carving sculptors create those absolutely clear blocks of ice by using a pump to keep the water (and any bubbles) circulating away from the center as the ice block freezes.


> Well, in general, the idea of getting the water to freeze from the outside inward would be the hard part. Where gravity exists (i.e. anywhere on earth) the water would freeze from the top down, because as individual bits if ice form, they would float upwards and accumulate at the top of the container, and you would never get a section of water completely surrounded by ice-- the bottom of the jar would be the last part to contain ice.
>

Gravity doesn't have anything to do with the fact that experimental bowls of water in the freezer tend to freeze from the top down. The reason they freeze in that fashion is because the open top is the surface most exposed to the chill zone. The only way that newly-formed ice crystals might float to the top is if they have been detached from the columnar crystallization zone by convection currents inside the mother liquor (i.e. in the liquid that is giving birth to solid crystals).


> To replicate the first system you describe (freezing from the outside inward) we would need to perform the experiment in 0-G.

No need for zero-gee, really. Just seal the water into a clear flexible plastic container, making sure there is no air headspace inside, and bury the entire container deep within a box of dry ice (solid carbon dioxide flakes). This will cool the 'outside-inwards' freezing system down at a decent clip.

Wolf "hydrocephalic" spirit